In an engine of the piston and cylinder type, it is necessary to charge each cylinder with a working fluid during the intake part of the engine cycle and to vent the fluid from the cylinder during the exhaust portion of each cycle.
In the case of an internal combustion engine, the working fluid injected into the cylinder is a fuel/air mixture and the fluid exhausted from the cylinder comprises the products of combustion of that fuel/air mixture. In the case of a uniflow steam engine, the working fluid is high pressure steam which is injected into the cylinder when the cylinder is at top dead center said steam being vented from the cylinder at the bottom of the piston stroke. Counterflow steam engines exhaust the steam through exhaust valves, in the cylinder head at top dead center. In all of these engines, the flow of the working fluid to and from the engine cylinders is controlled by intake and exhaust valves which open and close at the appropriate times during each cycle of each cylinder of the engine. In conventional gasoline engines, the valves are usually spring-loaded reciprocating valves which are opened and closed by cams on a rotary cam shaft, the cam shaft being rotated by the engine's crank shaft. Such reciprocating valves require a relatively large number of moving parts such as return springs, lifters, etc. Those valves are also prone to excessive wear and usually cause appreciable noise and vibration during operation of the engine.
State of the art steam engines employ variable cut-off throttles. Older, less efficient and less responsive steam engines employ fixed cut-off throttles. Fixed cut-off engines position the throttle in a position similar to that of the carburetor in an internal combustion engine. In a fixed cut-off system, a manifold connects the throttle to the cylinders. When the intake valve closes, steam is left in the manifold. The steam in the manifold loses heat energy and pressure decreases. If the driver backs off the throttle completely, causing it to close, the other cylinders remove the remaining steam from the manifold, wasting it. When the throttle is re-opened, the manifold must be re-filled with steam before the steam can enter the intake valves. Thus, leaving steam in the manifold during deceleration wastes energy.
In a variable cut-off system, the intake valves perform the throttle function. For the intake valves to meter the steam entering the cylinder, open valve time must be variable. In the past, this was accomplished by using two intake valves. Each valve was opened by a different cam. In order for steam to enter the cylinder, both valves had to be open at the same time. Such a multiple valve, multiple cam arrangement is complex and lacks precision.
To address such problems, it has been proposed to employ rotary valves to control the flow of the working fluid to and from the engine cylinders. For example, U.S. Pat. No. 4,944,261 discloses a spherical rotary valve assembly for an internal combustion engine. In accordance with that teaching, each engine cylinder requires two such assemblies, one to control the flow of the fuel/air mixture to the associated cylinder and the other valve to control the exhaust of the combustion products from that cylinder. Because the moving valve member of that valve assembly is a complicated 3-dimensional part, the assembly as a whole is difficult to manufacture and therefore relatively expensive. Bearing in mind that each engine may comprise 4, 6, 8 or more cylinders, each of which requires two such valve assemblies, the implementation of that patented construction adds materially to the overall cost of a typical engine.
In other conventional engines, complicated fuel injectors are used to inject the fuel into the engine cylinders at the appropriate times.
It would be advantageous, therefore, to be able to provide a simple, low cost valve assembly which can replace the reciprocating valves or injectors on a standard gasoline or diesel engine to enable that engine to run under steam power.